Magnesium-containing catalysts for ethylene (co)polymerization have been well known to provide significantly high catalytic activity and polymers having high bulk density, and also to be suitable for liquid and gas phase polymerization. Liquid phase polymerization of ethylene refers to a polymerization process conducted in bulk ethylene or a medium such as isopentane or hexane. In such liquid phase polymerization, catalyst properties such as high activity, shape, size, size distribution, bulk density, content of low molecular weight components that can be dissolved in a medium and the like are considered important, in terms of process applicability.
In the field of art where the present invention belongs, a variety of catalysts for olefin polymerization which contain magnesium and are based on titanium, and preparation processes thereof have been known. Particularly, many methods using a magnesium solution for obtaining a catalyst for olefin polymerization, which has high bulk density as mentioned above, have been known. There are methods for obtaining a magnesium compound solution by reacting a magnesium compound with an electron donor such as alcohol, amine, cyclic ether, organic carboxylic acid and the like, in the presence of a hydrocarbon solvent, for example, U.S. Pat. Nos. 3,642,746, 4,336,360, 4,330,649 and 5,106,807 wherein methods using alcohols are described. Further, many methods for preparing a magnesium-supported catalyst by reacting such liquid magnesium solution with a halogen compound such as titanium tetrachloride have been known in this field. Catalysts obtained from such methods of prior art, may provide high bulk density, however they are still needed to be improved in terms of catalytic activity or hydrogen reactivity. With respect to this, U.S. Pat. Nos. 4,477,639 and 4,518,706 describe inventions using tetrahydrofuran, i.e. cyclic ether, as a solvent for a magnesium compound.
U.S. Pat. Nos. 4,847,227, 4,816,433, 4,829,037, 4,970,186 and 5,130,284 describe methods for preparing a catalyst for olefin polymerization, which has excellent polymerization activity, and can provide polymers having improved bulk density, by reacting magnesium alkoxide with an electron donor such as dialkyl phthalate, phthaloyl chloride and the like, and with a titanium chloride compound.
U.S. Pat. Nos. 4,347,158, 4,422,957, 4,425,257, 4,618,661 and 4,680,381 describe methods for preparing a catalyst, wherein a catalyst is prepared by adding Lewis acids such as aluminum chloride to a magnesium chloride support and then pulverizing the resultant. Although catalytic activity has been complemented in the above-listed patents, they still have problems such that catalyst morphology such as shape, size and size distribution of a catalyst is irregular, and stereoregularity needs to be enhanced.
U.S. Pat. No. 5,459,116 describes a catalyst which can provide high polymerization activity and polymers having bulk density, wherein the catalyst is prepared by contact-reacting a magnesium compound solution containing esters having at least one hydroxyl group as an electron donor with a titanium compound, resulting in a supported solid titanium catalyst. However, it still needs to be improved in terms of particle morphology.